What are some classic examples of forces?

4 main types of forces

Gravity

Electromagnetic

Strong nuclear

Weak nuclear

How many forces are

acting on this frog

A. 1

B. 2

C. 3

D. 4

E. 5

"Could you explain more for me the correlation between mass and inertia?"

"What is a free body diagram?"

What forces are acting on a ball after it has been kicked and is rolling across the floor?

What forces are there on a car parked on a hill?

A jet is accelerating down the run way, what forces are acting on it? (don't neglect air resistance)

Mass is not weight, it is inertia

it is a resistance of motion for an applied force

Before we dive into F=ma

let us talk about kinematics and dynamics

this law relates the two.

The dynamics is what causes the motion

The kinematics is the resultant motion.

When something is moving it doesn't have multiple

accelerations. It has just one acceleration.

It can have multiple forces, but it will only have

one net or resultant force.

This distinction can help us as we add up all the forces.

If we find the direction of the one acceleration it will make solving the problems easier.

Newton's Second Law

Catch phrase:

F=ma

Stated: The acceleration of an object is directly

proportional to the net force acting on it, and

inversely proportional to its mass.

Nicer statement:

Are these the same?

Mathematically , Physically?

A Force is an action that can accelerate an object

Its SI units are Netwons , N

The base unit of a N comes from this 2nd law of motion

F =ma [N] = [kg][m/s ]

2

What net force would be required to bring a 2000 kg truck from rest up to 25 m/s in a time of 50 seconds?

Notice it is a vector equation

Thus it can be broken into components.

Also notice the sum, this means we have to

ADD all the different vectors together.

This is most effectively done in their individual components.

Stated:

Every object continues in its state of rest, or

uniform velocity in a straight line, as long as

no net force acts on it.

Newton's First Law of Motion

Catch phrase:

objects in motion stay in motion,

objects as rest stay at rest

Newton's First law is also known as

'the law of inertia'

What is inertia?

Mass is the measure of inertia.

The more mass something has

the more force is required to give it

some motion.

SI units : Kilogram , kg.

Is mass the same as weight?

Free-Body Diagrams

**THIS IS KEY**

Key parts to FBD

A. Particle

B. Coordinate system

C. All forces, note net force not on particle

Box pushed across a flat surface.

Car parked on a hill?

Bicycle picking up speed as it goes down a

hill.

Car going the same speed around a turn.

A cannon ball flying through the air (with no air resistance.)

A skydiver falling, and eventually reaching terminal velocity.

**Draw FBD of the following**

"I would like a better understanding of drag and thrust."

"Why does friction depend on the normal force? I also didn't understand too much the concept of inertia (with weight for example)."